1. Field of the Invention
The present invention relates to a hot reflow sputtering method and apparatus for filling holes formed in a substrate with a metallic material.
2. Description of the Related Art
Sputtering techniques that produce a desired thin film on the surface of a substrate by sputtering a target are often used in the production of semiconductor integrated circuits. In most cases, the semiconductor wafers on which thin films are formed have minute holes. As a result, it has been necessary to produce thin films inside these minute holes. For example, a DRAM (dynamic random access memory) with a capacity of 256 Mbit to 1 Gbit requires films to be deposited in channels and holes (referred to collectively as "holes" in the present specification) with a design rule or diameter of 0.25 .mu.m to 0.18 .mu.m.
Hot reflow sputtering, which fills in holes with a metallic material, is a practical mass-production technique that uses sputtering for the deposition of films inside such holes. FIG. 6 is a front view outlining the configuration of a conventional hot reflow sputtering apparatus that performs this sort of hot reflow sputtering.
The sputtering apparatus shown in FIG. 6 has a sputtering chamber 1 equipped with a pumping system 11 and a process gas introduction system 5 which introduces a process gas inside sputtering chamber 1. Inside sputtering chamber 1 are situated a target 2, which is provided so as to expose the surface 20 that is to be sputtered, a sputtering power source 3 for sputtering target 2, and a substrate holder 4 for positioning the substrate 9. A heater 6 is provided inside substrate holder 4 to heat substrate 9 to the desired temperature. Heater 6 is equipped with a control unit 7 which controls heater 6.
Target 2 is made of a metal such as aluminum, and is attached to sputtering chamber 1 via an insulating material 21. Sputtering power source 3 applies a large negative voltage to target 2. A process gas such as argon is introduced into sputtering chamber 1 by process gas introduction system 5. As the large negative voltage is applied to target 2, a DC field is established between the target and parts that are at ground potential, such as the substrate holder 4 and the walls of sputtering chamber 1. A sputtering discharge is caused by this DC field. Particles of the metallic material (usually in the form of atoms referred to as sputtered particles in this specification) that are discharged from target 2 by this sputtering discharge arrive at substrate 9, and a thin film of the desired metallic material is built up.
Meanwhile, the heat from heater 6 is applied to substrate 9 by way of substrate holder 4. Heater 6 is controlled by control unit 7 so that substrate 9 is kept at a fixed temperature. The thin film that has been built up on the surface of substrate 9 is fluidized (reflow) by the heat of substrate 9, and the minute holes are thereby filled in. As a result, the holes are filled in with metallic material, and the surface of substrate 9 is made smooth.
In the hot reflow sputtering mentioned above, the substrate must be heated to a high temperature of 400.degree. C. to 500.degree. C. or so. However, in conventional apparatus it is difficult to heat the substrate to such high temperatures in a short period of time--conventional apparatus has required a long processing time of at least 200 to 300 seconds or thereabouts, which has severely impaired the productivity.
As a result of investigating the configuration for heating the substrate, the present inventors have devised a configuration that allows the substrate to be heated rapidly. However, tests performed using this configuration have demonstrated that although the processing time can be reduced by rapid heating of the substrate, holes that should have been filled in with the metallic material end up containing cavities. or "voids" as they are known.